The present disclosure relates to a radio frequency radiation shield device, and more specifically, to an active radio frequency radiation shield device for transmitting nullifying signals.
Radio waves are used in a number of security access devices, such as remote keyless entry (RKE) vehicle devices and radio frequency identification (RFID) access cards, and such devices may need protection against incoming radio waves utilized in amplification, relay, or other forms of attacks used to operate the target equipment in ways it was not intended.
Taking the example of RKE, tens of millions of vehicles worldwide use this technology. A key fob is provided with a radio frequency antenna. When the driver touches the door handle for example, the car detects this and sends a low frequency message using near field communications to the key fob, which is usually on the driver. The key fob receives this near field communication and sends back a higher frequency message to the vehicle authorizing the unlocking of the vehicle doors. The same process is used for remote keyless start. When the driver sits in the vehicle seat and presses the start button, the car uses a near field antenna around the driver's seat to again send a near field message to the key fob, which in turn responds with a higher frequency message authorizing the vehicle to start the engine.
The security failing in this technology is that near field communications, which are radio frequency communications that operate in the near field utilizing transmission signals of very weak power to communicate, can be relayed or amplified. This invalidates the design assumption that near filed communications only work in close proximity. When a relay attack is used, a small near field receiver is used by an attacker when they approach the vehicle, their partner has the other end of the relay tool and points it to where the attackers believe the key fob is located inside a house. The relay receives the near field message, relays it to the other end of the tool, which then sends the message out with much higher power. The key fob receives the message and believes it must be near the vehicle so it sends back a message to authorize the action.
An amplification attack is similar, but simpler. A near field antenna on a wand is used by a first attacker and it is connected via a cable to the other end which is used by a second attacker with an amplifier. When the wand receives the message, the amplifier re-transmits it with much higher power. The same process then occurs where the key fob receives the message and authorizes the action.
A Faraday cage is a known form of protection in the form of an enclosure used to block electromagnetic fields. A Faraday cage is an enclosure formed by a continuous covering of conductive material or mesh. An external electrical field causes the electric charges within the cage's conducting material to be distributed such that they attenuate the field's effect in the cage's interior. This is used to protect sensitive electronic equipment from external radio frequency interference.
Faraday cages or Faraday bags that provide Faraday cage functions are expensive and the more they are used the less effective they become because of wear and tear to the seals. Also, discipline is required to always put a key fob or other device inside the Faraday bag. Furthermore, radio frequencies used in RKE or RFID are very hard to block as they are low frequency waves.